High capacity fluid pressure jack



W. A. RAPP HIGH CAPACITY FLUID PRESSURE JACK April 16, 1968 2 Sheets-Sheet 1 Filed Oct. 5, 1966 p y M 0 wk w w r A 7 ,mt. M M m w W w (my 4 m 4 0w 19 4 2 G F April 6, 1968 w. A. RAPP 3,378,231

HIGH CAPACITY FLUID PRESSURE JACK Filed Oct. 5. 1966 2 Sheets-Sheet 2 INVENTOR WALL/ICE A. RAPP BY WM W ATTORNEY United States Patent 3,378,231 HIGH CAPACITY FLUID PRESSURE JACK Wallace A. Rah l. 803 W. 10th St., Santa Ana, Calif. 92703 Filed Oct. 5, 1966, Ser. No. %,173 11 Claims. (Cl. 254--93) ABSTRACT OF THE DISCLOSURE A high capacity jack having a low clearance at one end when in the lowered condition, which jack has a horizontal frame having a first and a second end with a lift platform adjacent the first end, and having scissor link means including four parallel first links swingably connected at said one end of said frame and four second links each having a first end connected to the lift platform with a pin extending through the centers of all eight links to cause the links to swing relative to each other around that pin; said jack being further defined by a pair of pneumatic actuators connected to selectively force the second ends of said links apart as the actuators are extended to thereby raise the lift platform above the frame of the jack; and said jack being further defined by a mechanical safety device which will hold the jack in a raised position and the mechanical safety device has a paddle which is disposed such that air exhausting from the pneumatic actuators will move it from its locked position to an unlocked position to permit the jack to be lowered.

This invention relates to high capacity jacks, and more particularly to such jacks which have a very low clearance at the lifting end when the jack is in the collapsed, or lowered, condition.

A principal area of use of jacks incorporating the present invention is to raise the counterweight end of a fork lift. When it is desired to service a fork lift, little difficulty is encountered when it is desired to service the end of the fork lift which has the fork apparatus on it. In such case, the fork raiser post is merely tilted back and the forks are lowered suficiently that they will engage a block placed below them. Then tilting forward the raiser post will cause the forks to raise that end of the fork lift. Considerable difficulty is encountered in lifting the opposite end of the fork lift, which end has a heavy metal counterweight on it.

Firstly, the fork lifts are designed with very little clearance-only a few inches. Therefore, when the jack is in the lowered condition, the lifting end of the jack must have a very low clearance in order that it may be inserted underneath the counterweight. Further, because of the heavy weights involved, and the nature of some fork lifts, e.g., a short wheel base, it is extremely important that the jack lift is in a vertical line. That is, the lifting platform of the jack which engages the underside of the counterweight must rise in a vertical lin during the lifting operation. If the lifting platform were to swing in an arc, there is an increased danger that the jack will pull itself loose from the fork lift during the lifting operation. If the jack pulled itself loose from the fork lift, the jack would be kicked away from the fork lift causing possible injury to the operator. Further, the fork lift might be damage when it crashes to the floor.

Additionally, it has been found that it is quite often necessary to take the jack to the area where the fork lift is located. To this end, it is very desirable that the jack be light weight and easy to handle. Thereby, the repairman can carry the jack in his truck. to the scene of the fork lift, and then move the jack to the fork lift.

With the foregoing in mind, it is a major object of this invention to provide an improved high capacity jack.

Another object of this invention is to provide a high capacity jack which, when in the lower position, has a very low vertical clearance requirement at the lifting end of the jack.

A further object of this invention is to provide a jack which is light weight and portable in order that it may be fafsily transported to the object which it is desired to be i ted.

It is still another object of this invention to provide a light weight portable jack which has wheels for ease of positioning the jack, and has provision for automatically retracting the wheels during the lifting operation to provide a maximum distribution of the weight on the floor on which the jack rests.

At still further object of this invention is to provide an improved jack having a safety device which looks the jack in the raised position, and includes provision of means for automatically releasing the safety device at the time it is desired to lower the jack.

It is a still further object of this invention to provide a fluid powered jack including a plurality of fluid actuator cylinder-piston combinations in order to reduce the overall length and weight of the jack assembly.

It is still another object of this invention to provide a jack which uses fluid pressure actuators and includes means for driving the pistons of the fluid pressure actuators in both directions to facilitate operation of the jack.

A still further object of this invention is to provide a light weight low cost portable jack which is suitable for lifting the counterweight end of fork lifts.

Other and further objects of this invention will become apparent in the detailed description below in conjunction with the attached drawings wherein:

FIG. 1 is a perspective view of the preferred embodiment of a jack incorporating the present invention;

FIG. 2 is a side view of the jack shown in FIG. 1 in the raised condition;

IG. 3 is a side view of the jack shown in FIG. 1, shown in the lowered position;

FIG. 4 is an enlarged fragmentary cross-sectional view taken along line 44 in FIG. 2 disclosing the details of a preferred manner of mounting part of the scissor link assembly of the jack disclosed in FIG. 1;

FIG. 5 is an enlarged fragmentary view of the control valve means used to control the flow of the operating fluid pressure;

FIG. 6 is an enlarged fragmentary view of a portion of the jack disclosing the manner in which the safety lock means operates to prevent accidental collapsing of the jack disclosed in FIG. 1;

FIG. 7 is an enlarged fragmentary view of a portion of the jack disclosing the manner in which the safety lock means operates before the jack is completely raised; and

FIG. 8 is an enlarged fragmentary cross-sectional view taken along line 88 in FIG. 1 disclosing details of the manner in which the lift platform is mounted.

Referring now to the drawings, the jack includes a frame, indicated generally by the arrow 10, with scissor link means, indicated generally by the arrow 11, which selectively raise a lift platform 12 through the use of ram means in the form of fluid pressure actuators, indicated generally by the arrow 13. As will be described, when fluid pressure is supplied to the actuators 13 a plunger (formed by a piston with a piston rod projecting from the cylinder) in each of them is extended. This action raises the lift platform 12thus raising any weight located on the lift platform.

Referring now to the preferred embodiment in more detail, it can be seen that the frame includes a pair of channel member rails 16 which are fixed at their ends by cross members 17. Handles 18 are provided near the actuator end of the frame at the balance point for ease of lifting the jack off of the floor into, for example, a truck.

In the illustrated embodiment of the invention, the scissor link means 11 includes four first elongated links 19. At their respective first ends, the links 19 are each pivotally connected to the frame 10 by means of a clevis 20, and a bolt 21 which is received through a hole at the respective end of the link. The manner of mounting the second end of each of the links 19 will be described later. The scissor link means 11 also includes a set of second elongated links 23. As can be seen, the links 19 and the links 23 are swingably secured at their respective center portions by means of an axle bolt 24 extending through all eight links. For purposes of stability, tubular spacers 25 are provided as shown.

Referring now to FIGS. 1, 2, and 8, the manner in which the links 23 are secured to the lift platform 12 will be described in further detail. At the first end of each link 23 there is positioned a clevis 27 which receives through its aligned holes-and a corresponding hole in the end of the linka shoulder bolt 28. Thereby, the lift platform 12 is permitted to rotate with the, for example, counterweight of the fork lift during the lifting operation.

As has been mentioned previously, it is very important that the lift platform 12 rise in a vertical line during the lifting operation. To this end, the second ends of the links 23 are mounted in a manner which will now be described. Referring now to FIG. 4 in particular, it can be seen that the channel member rails 16 each form inwardly facing tracks. Therefore, axle 30 may travel along the channel member rails 16 through the use of steel rollers 31 which have ball bearings because of the loads involved. The second ends of the links 23 are swingably connected to the axle 30 by receiving the axle through holes located in the second ends of the respective links. Similarly, piston rods 33 of the actuators 13 have holes in their extreme ends through which is received the axle 30. Spacers 34 are provided so that the various components will retain their designed orientation.

Referring back to FIGS. 1 to 3, it can be seen that the actuators 13 include cylinders 36 out of which extend the piston rods 33. Additionally, at the bottom of each cylinder 36 there is provided a pair of trunnions, or stub shafts, 37 each of which is received through a hole in the second end of a respective first link 19. Appropriate cotter pins are used for retaining the links 19 on the trunnions 37.

With the structure thus far described, it can be seen that the lift platform 12 can be raised by supplying fluid pressure, preferably pneumatic pressure, to the upper side of the pistons in the cylinders 36--thus extending the piston rods 33. Such extension of the piston rods causes the trunnions 37 to rise with the cylinders 36 raising the second ends of the links 19. Through the connection afforded by the axle 24, the center of the links 23 is also raised since the second end of the links 23 is constrained against vertical movement by the channel members 16 .4 and the downward force of the piston rods 33. Therefore, the lift platform 12 rises. It should be particularly noted that during the raising operation the axle 30, and therefore the second ends of the links 23, move to the right, which action is freely permitted because of the provision of the rollers 31. (Compare FIG. 2 to FIG. 3.) Because of the foregoing, it will be noted that the lift platform 12 rises in a vertical line. To facilitate illustration of this, the vertical center lines of the bolts 21 and the bolts 28 have been extended in FIGS. 2 and 3. It can be seen that the lateral distance between the center lines is the same when the jack is in the raised position (see FIG. 2) as when the jack is in the lowered position (see FIG. 3). Dimensional arrows 38 pointing to said vertical center lines, have been included in FIGS. 2 and 3. It should be particularly noted that the actuators apply their forces in a very efficient manner. More particularly, by pressing down on the second ends of the links 23 and pulling up on the second ends of the links 19 the links are loaded so as to transmit the maximum upward force to the lift platform 12 with the minimum amount of stresses on the links.

Before turning to the detailed description of the manner in which the operating fluid issupplied and controlled, another feature of the preferred embodiment will be pointed out, to wit, provision of dual actuators. It takes a great deal of force to lift a fork lift counterweight because of the large weight involved. Therefore, in order to permit the use of less expensive (as compared to hydraulic actuators) pneumatic actuators, a large amount of operating piston area is needed. If only one actuator 13 were used, it would have to be of over 40% larger diameter than if two actuators were used. It has been found, that the use of a single actuator requires the jack to be longer. This makes the jack more difiicult to use because of the weight involved and because the jack is more easily handled when it is more nearly square. Additionally, not much reduction in width of the frame 10, i.e., the distance between the rails 16 would -be permitted through the use of a single actuator since the lateral dimensions are needed for stability.

Referring now to FIGS. 1, 2, 3, and 5, the manner in which the operating fluid will be described in further detail. In the preferred embodiment compressed air is the operating fluid. Air is supplied through a conventional quick release connector 40 (see PEG. 5), and thence through a T joint 41 to the input side of a three-way valve, indicated generally by the arrow 42. From the valve 42 compressed air is supplied through a riser pipe 43 to header pipes 44 (see FIG. 1), and then to the cylinders 36 through right angle fittings 45.

In order to operate the valve 42, there is provided an actuator lever 46 which is pivotally mounted on an upstanding bifurcated support by means of a pin 47. When the handle portion (the left end as seen in FIG. 5) of the lever 46 is raised, the lever engages a pin 48 in the valve 42 and opens the input side of the valve 42. This will cause air to flow upwardly through the pipe 43 and thence into the top side of the pistons in the cylinders 36 through the header pipes 44. Such air will drive the pistons downwardly raising the jack.

When it is desired to lower the jack, the handle portion of the actuator lever 46 is lowered. First, the pin 48 returns to its original position closing the inlet side of the valve 42. Then, further depressing of the handle portion of the lever 46 causes the lever to engage a pin 49 on the outlet side of the valve 42. This permits the air on the top of the pistons in the cylinders 36 to exhaust through the pipes 44 and 43 and thence out through a discharge port 50 in the valve 42. The air discharging through the port 50 is a blast illustrated by hidden lines 50a. The preferred manner in which this blast of exhaust air is used in the operation of the jack will be described in further detail below.

As the cylinders required are fairly large, in the order of 8 inches in diameterand for an additional purpose pointed out below-it is preferred that the jack be returned to the lowered condition by positive fluid pressure. To this end, air is tapped off of the joint 41 and led through a connector pipe 51 to a valve 52 secured to the underside of support plate 53 which is fixed to the cylinders 36. From the valve 52, air is selectively directed through a connector pipe 54, and thence through a header pipe 55 to each respective cylinder 36 through a respective right angle fitting 56 (see FIGS. 2 and 3). It will be noted that the valve 52 has an actuator button 57 extending up through the support plate 53. With the arrangement disclosed, further depressing of the actuator lever 46 can open the valve 52 to supply air to the underside of the piston in each respective cylinder 36 to retract the piston rods 33.

By design, air is permitted to leak from the cylinder below the piston by provision of a non-sealing bearing support between the piston rod and the hole in the cylinder bottom end wall through which the piston rod passes. However, the leak is at a much slower rate than the influx of air when the valve 52 is opened.

The relationship of the actuator lever 46, the pins 48 and 49, and the button 57 will now be described. As mentioned previously, the operator merely raises the handle portion of the lever 46 to thereby raise the pin 48 to supply air pressure into the upper side of the cylinders 36. When the operator desires to lower the jack, he depresses the handle portion of the lever 46. During such counterclockwise movement (as seen in FIG. 5), the right end of the lever 46 engages and raises the pin 49 thus exhausting the upper side of the cylinders 36. At this point, if there were no weight on the jack, the jack would not lower because of the friction between the pistons and cylinder walls of the seals of the relatively large pistons in the cylinders 36. However, continued downward movement of the left end of the actuator lever 46 causes it to engage the button 57 to supply air to the under side of the pistons in the cylinders 36. During this step, the pin 49 is moved further upward-which movement is permitted by the design of the valve 42.

As mentioned previously, it is desired that means be included for mechanically locking the jack to prevent it from moving from the raised condition except at the desired times. Referring now to FIGS. 1, 2, 5, 6, and 7, a preferred form of such lock means will now be described. As can be seen best in FIGS. 6 and 7, there is provided a latch member 60 which is swingably mounted on a pin, or axle, 61 which is press fit into the centrally disposed second links 23. For purposes of stability of the latch member 60, it is welded to a journal bearing pipe section 62 which spaces the latch member from the links 23 and stabilizes its arc of motion. Toward its upper end, the latch member 60 has a step, or notch 63 with an upstanding portion 64 extending upwardly from the step 63. At the upper end of the portion 64 there is a spoon, or paddle, 65 for a purpose which will be described in a moment. Said paddle 65 has a concave surface juxtapositioned to said discharge port 50.

Also extending between the centrally disposed links 19, there is a stop 67 positioned in proximity to the step 63 when the jack is in the raised condition.

It is desired that the latch member 60 be urged in a direction to move the step 63 into the path of descent of the stop 67 when the jack is being lowered. To this end, there is provided a spring 68 connected between a pin 69 on the particular link 23 shown in FIG. 6 and a hook 70 on the latch member. This spring 68 tends to rotate the latch member 60 counterclockwise (as seen in FIGS. 6 and 7).

The manner in which the lock means operates will now be described. The latch member 60 moves between a first position such as shown in FIG. 6 where the step 63 is in the path of descent of the stop 67 and a second position (such as shown in FIG. 7) where the step 63 is out of such path. As the jack is being raised, the spring 68 urges the latch member 60 counterclockwise (as seen it FIG. 7) against the stop 67. Finally, as the jack approaches its full raised condition, the stop 67 raises above the step 63 allowing the latch member 60 to rotate further to the position shown in FIG. 6--where furthel counterclockwise rotation is stopped by engagement of the upstanding portion 64 with the stop 67. In such condition, if there were pressure failure in the actuators 13, the jack would only descend until the stop 67 engages the step 63.

It will be noted that the spoon, or paddle, 65 is disposed immediately in front of the exhaust port 50. By this placement, when the operator depresses the actuator lever 46 to open the exhaust side of the valve 42, air blasting out of the port blows the paddle 65 to the right, pushing the step 63 of the latch member out of the path of descent of the stop 67. This permits the jack to be lowered at the desired time without manually pushing the latch member 60 out of the locked position. As can be seen, such automatic releasing of the safety lock mechanism simplifies and speeds completion of the job.

Another aspect of the present invention is that it has wheels for facilitating movement of the jack on the floor, however, the wheels retract during the lifting operation. This is important in order to spread on the floor supporting the jack the load of the heavy weight being lifted, and to eliminate the need of an extremely heavy duty wheel system. With the present invention, the wheeled support can be easily accomplished by provision of two wheels 72 which are rotatably mounted on stub shafts 73 welded to the outside links 23. In FIG. 1 nut 74 which secures the far (as seen in FIG. 1) wheel 72 onto the stub shaft can be seen.

With the provision of the positive fluid pressure retracting the piston rods 33, the jack is moved to the lowered condition shown in FIG. 3. And, as shown in FIG. 3, the wheels 72 extend below the frame 10. The operator can quickly position the jack by balancing it on the wheels 72 and steering the jack by a light touch in the area of the header pipes 44. The friction between the seals of the actuator pistons and the interior walls of the cylinders 36 is suflicient to prevent the wheels from retracting from their depending position after the air pressure is removed. However, it can be seen, that it is very desirable that the positive fluid pressure be available to force initially the jack into the lowered position where the wheels 72 project and support the jack.

On the other hand, the jack need be raiesd very little before the wheels 72 are retracted and the load is distributed over all of the bottom surfaces of the frame forming the wide base of the jack.

While only a few embodiments of the present invention have been shown and described in detail, it will be apparent to those skilled in the art that such is by Way of illustration only and numerous changes may be made thereto without departing from the spirit of the present invention. Accordingly, it is my intention that the present invention be limited solely by the appended claims.

I claim:

1. A high capacity jack having a low clearance at one end when in the lowered condition, said jack comprising: a horizontal frame having a first and a second end;

a lift platform adjacent said first end;

scissor link means including:

a first elongated link having a first end swingably connected to said one end of said frame and a second link having a first end connected to said lift platform, said second link having a second end operatively connected to said frame for horizontal movement along said frame as said links are moved between a lowered and raised position;

means connecting said links together at a center portion of each link for swinging movement between a lowered position generally parallel to each other and a raised position more normal to each other than when in said lowered position, said scissor link means raising said lift platform above said frame as the elongated links are moved toward said raised position;

and fluid pressure actuator means including a cylinder and an extendable plunger for moving said links toward said raised position as said plunger is extended, one of said plunger and cylinder being connected to a second end of said first link and the other of said plunger and cylinder being connected to said second end of said second link, whereby there is a low clearance at said one end of said frame when said links are in said lowered position and said lift platform is moved in a vertical line when said links are moved toward said raised position by extention of said plunger.

2. The jack set forth in claim 1 wherein:

said plunger is connected to said second end of said second link and said cylinder is connected to said second end of said first link, and said cylinder projects above said second ends of said links.

3. The jack set forth in claim 1 wherein said plunger is extended by fluid pressure in said cylinder, and includmg:

lock means for maintaining said links in said raised position, said lock means including:

a stop on one of said first and second links;

a latch member movably secured to the other of said first and second links for movement between a locked position in the path of the movement of said stop as the links are moved from said raised position toward said lowered posi tion and an unlocked position out of the path of said stop when said links are moved from said raised position toward said lowered position;

and means normally urging said latch member toward said locked position;

and release means on said jack for causing said latch member to move from said locked position to said unlocked position when said fluid pressure is exhausted from said cylinder, whereby said lock means prevents movement of said link from said raised position until said fluid pressure is exhausted.

4. The jack set forth in claim 3 wherein said release means includes:

an exhaust port connected to said cylinder through which said fluid pressure in said cylinder is exhausted;

and a portion of said latch member disposed in front of said exhaust port for movement away from said port due to the force on said last mentioned portion of fluid exhausting through said port, said last mentioned latch member being disposed so that fluid pressure exhausting through said port and striking said last mentioned portion urges the latch member toward said unlocked position.

5. The jack set forth in claim 1 including:

a wheel rotatably mounted on one of said first and second links, said wheel extending below said frame when said links are in said lowered position for supporting said frame for movement along the ground.

6. The jack set forth in claim 5 including:

fluid pressure means connected to said cylinder for selectively urging said links toward said lowered position.

7. The jack set forth in claim 6 including:

a piston within said cylinder connected to said plunger;

first control means for supplying fluid pressure on one side of said piston to extend said plunger and exhaust said fluid pressure;

second control means for supplying fluid pressure on the other side of said piston to return said plunger;

and master control means for controlling said first and second control means, said master control means causing said fluid pressure to exhaust from said one side of said piston before pressure is supplied to said other side of said piston. 8. The jack set forth in claim 2 wherein said second end of said first link is connected to said cylinder on one side thereof;

and including a second scissor link means, said second link means including:

a first elongated link having a first end swingably connected to said one end of said frame at a point spaced from said first link of said first mentioned scissor link means and a second end connected to said cylinder on a side opposite the point of connection of the second end of said first link of said first mentioned scissor link means;

a second elongated link having a first end con nected to said lift platform at a point spaced from said second link of said first mentioned scissor link means and a second end operatively connected to said frame for horizontal movement along said frame as said links are moved between a lowered position generally parallel to each other and a raised position more normal to each other than said lowered position, said last mentioned scissor link means raising said lift platform above said frame as the elongated links are moved toward said raised position as said plunger is extended.

9. The jack set forth in claim 8 including:

second fluid pressure means including a cylinder and an extendable plunger, said second fluid pressure means being located at the end of said frame opposite said one end;

third and fourth scissor link means connected to said frame, said lift platform, and said second fluid pressure means for raising said lift platform in response to extention of said last mentioned plunger.

10. A jack comprising:

a frame having a first and a second end;

a lift platform disposed near said first end of said frame;

mechanical linkage means connected to said frame and said lift platform for raising said platform as said mechanical means is moved from a first position to a second position, said mechanical linkage means extending from first end to said second end when in said first position; and fluid pressure means including a cylinder and an extendable plunger, said plunger and cylinder being operatively connected to said mechanical linkage means at two separate points on said linkage means for moving said linkage means to said second position as said fluid pressure means extends said plunger and moves said two separate points apart, said fluid pressure means being located entirely at said second end and said two separate points being in proximity to said second end, whereby said fluid pressure means does not obstruct the first end or the center part of the frame.

11. A jack comprising:

a frame;

a lift platform operatively connected to said frame;

fluid pressure operated means including a cylinder and an extendable plunger movable between two positions, said means being operatively connected to said frame and said lift platform for raising and lowering said lift platform relative to said frame as said plunger is moved between said two position;

control means for selectively supplying air pressure into said cylinder on one side of said plunger for causing said plunger to move from one of said two positions to the other of said two positions to raise said lift platform relative to said frame;

an exhaust port communicating with the cylinder on said one side of said plunger through which air in said cylinder on said one side of said plunger may be selectively rapidly exhausted;

lock means for locking said jack in a raised condition,

said lock means including:

a latch member disposed for movement between a first position where it prevents said jack from being lowered from a raised condition and a second position where it does not prevent the jack from being lowered;

and means disposed in front of said exhaust port for moving said latch member from said first position to said second position in response to air being rapidly exhausted through said exhaust port.

References Cited.

UNITED STATES PATENTS r 3,174,722 3/1965 Alm 187-18 X 3,195,860 7/1965 Simms 254-2 FOREIGN PATENTS 742,439 3/1933 France. 1,100,403 4/ 1955 France.

OTHELL M. SIMPSON, Primary Examiner. 

